import的疑问

[cashlu]

说明：下面有三段代码，实际上后两段代码是将第一段代码拆分成两个java文件保存了，实现功能完全一样
问题：就我的理解，import java.util.*的作用是引入util下所有的类库，但是在第一段代码中，我还必须专门引入Date，否则编译就会报错，但如果像后两段代码一样，拆分开的，不用再单独的引入Date，一样可以编译成功，这是为什么？谢谢！

代码1：

import java.util.Date;
import java.util.*;

public class EmployeeTest
{
	public static void main(String[] args)
	{
		Employee[] staff = new Employee[3];
		
		staff[0] = new Employee("Simon Lo",2450,2006,8,25);
		staff[1] = new Employee("Seven Huang",3500,2006,06,01);
		staff[2] = new Employee("Eric Yap",5000,2000,01,15);

	
		for (Employee e : staff)
			e.raiseSalary(5);
	
		for (Employee e : staff)
			System.out.printf("\nName=" + e.getName() + "\nSalary=" + e.getSalary() + "\nHireDay=" + e.getHireDay());
	}
}

class Employee
{
	public Employee(String n, double s, int year, int month, int day)
	{
		name = n;
		salary = s;
		GregorianCalendar calendar = new GregorianCalendar(year, month -1, day);
		hireDay = calendar.getTime();
	}
	
	public String getName()
	{
		return name;
	}
	
	public double getSalary()
	{
		return salary;
	}
	
	public Date getHireDay()
	{
		return hireDay;
	}
	
	public void raiseSalary(double byPercent)
	{
		double raise = salary * byPercent / 100;
		salary += raise;
	}
	
	private String name;
	private double salary;
	private Date hireDay;
}

代码2：

import java.util.*;
class Employee
{
	private String name;
	private double salary;
	private Date hireDay;
	
	public Employee(String n, double s, int year, int month, int day)
	{
		name  = n;
		salary = s;
		GregorianCalendar calendar = new GregorianCalendar(year,month - 1,day);
		hireDay = calendar.getTime();
	}
	
	public String getName()
	{
		return name;
	}
	public double getSalary()
	{
		return salary;
	}
	public Date getHireDay()
	{
		return hireDay;
	}
	
	public void raiseSalary(double byPercent)
	{
		double raise = salary * byPercent /100;
		salary = salary + raise;
	}
	
	
	//下面的main方法是用来测试Employee类的，并不会在整个程序中执行
	public static void main(String args[])
	{
		Employee test = new Employee("Simon Lo",3000,2006,8,1);
		test.raiseSalary(10);
		System.out.println("There is some Unit Test blow this line:");
		System.out.printf(test.getName() + "\t" + test.getSalary());
	}

}

代码3：

import java.util.*;

public class EmployeeTest
{
	public static void main(String args[])
	{
		Employee[] staff = new Employee[3];
		
		staff[0] = new Employee("Carl Cracker", 75000, 1987, 12, 15);
		staff[1] = new Employee("Harry Hacker", 50000, 1989, 10, 1);
		staff[2] = new Employee("Tony Tester", 40000, 1990, 3, 15);
		
		for (Employee e : staff)
			e.raiseSalary(5);
		
		for (Employee e : staff)
			System.out.printf("Name=" + e.getName() + "\tsalary=" + e.getSalary() + "\thireDay=" + e.getHireDay() + "\n");
	}
}

[wd9053]

我的机器上第一个去掉import java.util.Date才编译通过。
我估计是在classpath中还有其他的Date类而且排名在jdk前面
如：classpath = .;**\JDK1.6\lib\dt.jar;....
如果在当前路径中存在自己定义的Date类文件，那么会报错
EmployeeTest.java:29: 不兼容的类型
找到： java.util.Date
需要： Date
hireDay = calendar.getTime();

[cashlu]

哈哈哈……楼上的哥们儿！太感谢了！正如你所说的，同目录下存在一个Date.class文件！
非常感谢！